1. Field of the Invention
The present invention relates to a resin composition comprising a mixture of one or more polyamide resins and one or more ethylene/vinyl alcohol copolymers. More particularly, the present invention relates to a resin composition suitable for manufacturing into a film, which is improved in flowability during processing and in which formation of gel product is suppressed.
2. Description of Related Art
Polyamide resins have been widely used in various fields due to their favorable properties such as toughness, anti-pinhole property, gas barrier property, heat resistance and so on. Concerning these properties, however, specifically the gas barrier property, the polyamide resins by themselves are not always satisfactory and their application is limited to fields in which a higher gas barrier property is not required.
Ethylene/vinyl alcohol copolymers are resins known to have a gas barrier property superior to that of the polyamide resins. While ethylene/vinyl alcohol copolymers are certainly superior in gas barrier property, they are deficient in that formed products thereof are hard and fragile and thus susceptible to fracture and pinhole formation, for example, when used in the formation of films, and particularly during packaging and transfer or transport of packaged products when they are used as a film or sheet for food packages. Therefore, their superior gas barrier property has not been made of good use.
Japanese patent applications, JP-B-44-24277, JP-B-48-22833 and JP-A-55-34956, the disclosures of which are hereby incorporated by reference, proposed to produce formed products such as films making favorable use of the good points of both polyamide resins and ethylene/vinyl alcohol copolymers, i.e., the gas barrier property of the ethylene/vinyl alcohol copolymers and the heat resistance and anti-pinhole property of the polyamide resins, by mixing a polyamide resin and an ethylene/vinyl alcohol copolymer.
While the gas barrier property of the polyamide resins could be improved by blending an ethylene/vinyl alcohol copolymer into a polyamide resin, a new problem arose that the polyamide resin and the ethylene/vinyl alcohol copolymer chemically reacted during processing, i.e., while in a processing machine such as an extruder, to form an undesirable gel product which remained in the final product such as a film. Because the problem of gel formation becomes more remarkable as the forming temperature becomes higher, laid open Japanese patent applications, JP-A-54-78749 and JP-A-54-78750, the disclosures of which are hereby incorporated by reference, proposed the use of a low melting copolymeric polyamide which allows for forming at a lower temperature.
Since, however, there is a limit in the prevention of gelling, even if a copolymeric polyamide is used, the development of a resin composition wherein gelling is reduced without deteriorating processability in the molding of a mixture of a polyamide resin and a ethylene/vinyl alcohol copolymer is strongly desired.
The resin composition of the present invention is the result of extensive studies conducted by the present inventors for improving stability in the processing of a mixture of one or more polyamide resins and one or more ethylene/vinyl alcohol copolymers, for example, for solving the problem of fish eye gel formation in the processing of the resin composition into a film.